1. Field of the Invention
The present invention relates to a single-application polyimidosiloxane-based coating material containing an organic solvent-soluble polyimidosiloxane, an epoxy resin and a fine organic filler, and to a cured film obtained by heating the coating material.
The coating material of the invention has satisfactory storage stability and printing properties, gives cured films with satisfactory plating resistance (for example, tin resistance, tin burrowing resistance) and can be applied in a single application.
Also, the cured films of the invention have adhesion to substrates, flex resistance, heat resistance (for example, bump connection heat resistance and soldering heat resistance) and electrical properties, as well as plating resistance properties (for example, tin resistance and tin burrowing resistance), and can therefore be utilized as electrically insulating protective films.
Throughout the present specification, xe2x80x9csingle-applicationxe2x80x9d will be used to mean a system wherein protection by a double-application coating material composed of two different insulating materials, one a plating resistant epoxy dam (Long periods are required for formation of epoxy dams.) employed to protect the wiring pattern of an IL (inner lead) and an OL (outer lead) of an electronic part subjected to TAB (tape automated bonding) or the like, and the other a polyimide-based coating material as a protective insulating film, is achieved with a coating material of a single type of insulating material.
Thus, according to the invention it is possible to eliminate one step with respect to conventional double-application coatings while achieving an equivalent or better function.
2. Description of the Related Art
Conventional uses of known aromatic polyimides, epoxy resins and so forth as electrical insulating protective films include such uses as insulating films for solid elements and insulating films for semiconductor integrated circuits, flexible wiring boards and the like.
Epoxy resins are used as epoxy dams because of their plating resistance and satisfactory adhesion with substrates, but they also require the use of curing agents, etc., which have presented various problems involving the storage stability of the curing agents and the operations-for two-part solution preparation, and when used as insulating films as mentioned above, the insulating films formed by thermosetting are rigid, have low plasticity and lack flex resistance.
Also, because aromatic polyimides are generally poorly soluble in organic solvents, a solution of an aromatic polyimide precursor (aromatic polyamic acid) must be used to form a coating film, subsequently accomplishing drying and imidation by heat treatment at high temperature over a long period to form an aromatic polyimide protective film, and this presents the problem that the electrical or electronic member itself, which is to be protected, undergoes heat deterioration.
On the other hand, aromatic polyimides which are soluble in organic solvents are known from, for example, Japanese Examined Patent Publication No. 57-41491 which describes an aromatic polyimide prepared by polymerizing and imidating a biphenyltetracarboxylic acid and a diamine compound in an organic polar solvent; however, since this polyimide does not have sufficient cohesion (adhesion) with silicon wafers, glass panels, flexible substrates and the like, it requires a process whereby the substrate is pretreated with an adhesion promoter.
It is an object of the present invention to provide a coating material which has storage stability and printing properties, the cured films of which possess the properties of plating resistance (tin resistance, tin burrowing resistance), heat resistance and plasticity, and which allow single-application coating, as well as cured films thereof.
In other words, the present invention provides a single-application polyimidosiloxane-based coating material which comprises
(a) 100 parts by weight of an organic solvent-soluble polyimidosiloxane represented by general formulae (1) to (3) 
wherein R1 is a tetravalent residue resulting from removal of the 4 carboxyl groups from an aromatic tetracarboxylic acid, R2 is a divalent residue resulting from removal of the amino groups from a diaminopolysiloxane represented by general formula (4) below, R3 is a divalent residue resulting from removal of the amino groups from an aromatic diamine compound represented by general formula (5) below, R4 is a divalent residue resulting from removal of the amino groups from a diamine compound other than a diamine compound represented by general formulae (4) and (5) below, n, is 3-50, each R5 is a divalent hydrocarbon group or phenyl group, each R6 is independently an alkyl group of 1-3 carbon atoms or a phenyl group, X is a direct bond or a group selected from the groups represented by general formulae (6) below, r, is a hydroxyl group or carboxyl group, n2 is an integer of 1 or 2, n3 is an integer of 0-3, R7 and R8 are hydrogen, methyl groups or trifluoromethyl groups, and m1, m2 and m3 are in a proportion such that of the total 100 mole percent of the components, m1 constitutes 60-92.5 mole percent, m2 constitutes 7.5-40 mole percent and m3 constitutes the remainder; 
(b) 2-30 parts by weight of an epoxy resin;
(c) 20-150 parts by weight of a fine inorganic filler; and
(d) 60-140 parts by weight of a high-boiling-point solvent, and which has a viscosity of 400-1000 poise.
The invention further provides a cured film prepared by coating, heating and drying a single-application polyimidosiloxane-based coating material comprising the components listed above on the pattern surface of an electronic part having an insulating film and a conductor-formed pattern thereon.
The invention still further provides a single-application polyimidosiloxane coating material which is obtained by uniform mixing of a polyimidosiloxane including an epoxy resin-reactive functional group, an epoxy resin and a fine inorganic filler in a high-boiling-point solvent, which is printable, and which upon heating and drying gives a cured film with an elastic modulus of 0.1-20 kg/mm2 and tin burrowing of 100 xcexcm or less.
The invention still further provides a cured film prepared by coating, heating and drying a printable single-application polyimidosiloxane coating material, which is obtained by uniform mixing of a polyimidosiloxane obtained using an aromatic diamine including an epoxy resin-reactive functional group, an epoxy resin and a fine inorganic filler in a high-boiling-point solvent, on the pattern surface of an electronic part having an insulating film and a conductor-formed pattern thereon, the cured film having an elastic modulus of 0.1-20 kg/mm2, and tin burrowing of 100 xcexcm or less, and preferably 10-100 xcexcm